response; again, radar is best suited for this difficult volume search and incoming threat location challenge.

Counter-IED sensor systems generally seek to find the threat and any details about its emplacement. In this sense, counter-IED benefits from ISR system products, such as change detection outputs and subsidence measurements. From the squad perspective, however, some capability for rapid determination of likely IED emplacements is essential. For example, a sensor system to scan and determine whether cordoned culverts have been tampered with would prove invaluable to a squad. Similarly, the ability to remotely scan and determine the presence of CBRN and mines is another key to force protection. A likely strategy for CBRN agent detection is to remotely interrogate sensors whose properties (e.g., radar cross section, resonance, luminescence) change when exposed to the target agent; radar, laser, and IR sensors are applicable technologies. Ground penetrating radar and hyper- or multispectral imagers can be used to detect disturbed soil and find buried mines at limited depths; such sensors exhibit variable performance depending on soil properties.

Rapidly determining the general location of hostile fire provides the squad with time to take cover and prepare to return fire. Of the technologies available to determine shot location, acoustic sensors appear best. IR sensors can detect muzzle flashes, but the search problem is challenging, and background clutter is a concern. The small radar cross section of a bullet renders radar less useful in this particular case. Multipath in urban and mountainous terrain is a limiting factor for acoustic-based hostile fire indication systems.

Precision Targeting

Squad-level precision targeting objectives include the following:

•   Solutions against batteries of rockets, artillery, or mortars;

•   Counterfire solutions against small arms;

•   Vehicle engagement with high probability of kill; and

•   Concealed threat targeting.

WLR systems employ target tracks and kinematic models to estimate the location of the hostile fire. This counterbattery solution is then used to return fire. Acoustic sensors are the likely choice to locate small arms fire; time-difference of arrival among several microphones, for example, can be used to determine the threat location. Vehicle engagement can involve fixed or moving targets detected by radar, FMV, WAMI, or IR sensors. Given likely constraints on squad engagement ranges, a multimode seeker fusing radar, laser, and IR sensors will provide the most robust solution. Concealed threat targeting could involve formulating a fire control solution against targets behind walls or abutments; the ability to engage unseen targets is clearly a decisive advantage for the squad. In each of the aforementioned cases, system calibration is critical to achieving the



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